This article is about the organism. For the infection, seePinworm infection.
This article is about the nematode of the family Enterobius, known as pinworm in the US. For the different nematode known as pinworm in the rest of the world, seeStrongyloides stercoralis.
Other than human,Enterobius vermicularis were reported frombonnet macaque.[10] Other species seen inprimates includeEnterobius buckleyi inOrangutan[11] andEnterobius anthropopitheci inchimpanzee.Enterobius vermicularis is common in human children and transmitted via the faecal-oral route. Humans are the only natural host ofEnterobius vermicularis.[12]Enterobius gregorii, another human species is morphologically indistinguishable fromEnterobius vermicularis except thespicule size.[13] Throughout this article, the word "pinworm" refers toEnterobius. In British usage, however, pinworm refers toStrongyloides, whileEnterobius is called threadworm.[14]
The pinworm (genusEnterobius) is a type ofroundworm (nematode), and three species of pinworm have been identified with certainty.[15] Humans are hosts only toEnterobius vermicularis (formerlyOxyurias vermicularis).[16]Chimpanzees are host toEnterobius anthropopitheci, which ismorphologically distinguishable from the human pinworm.[5] Hugot (1983) claims another species affects humans,Enterobius gregorii, which is supposedly asister species ofE. vermicularis, and has a slightly smallerspicule (i.e., sexual organ).[17] Its existence is controversial, however; Totkova et al. (2003) consider the evidence to be insufficient,[6] and Hasegawa et al. (2006) contend thatE. gregorii is a younger stage ofE. vermicularis.[4][5] Regardless of its status as a distinct species,E. gregorii is considered clinically identical toE. vermicularis.[16]
Two female pinworms next to a ruler: The markings are 1 mm apart.
The adult female has a sharply pointedposterior end, is 8 to 13 mm long, and 0.5 mm thick.[18] The adult male is considerably smaller, measuring 2 to 5 mm long and 0.2 mm thick, and has a curved posterior end.[18] The eggs aretranslucent[18] and have a surface that adheres to objects.[19] The eggs measure 50 to 60μm by 20 to 30 μm, and have a thick shell flattened on one side.[18] The small size and colourlessness of the eggs make them invisible to the naked eye, except in barely visible clumps of thousands of eggs. Eggs may contain a developingembryo or a fully developed pinwormlarva.[18] The larvae grow to 140–150 μm in length.[19]
Life cycle ofE. vermicularis showing the stages inside and outside of the human body
The entire life cycle, from egg to adult, takes place in thehuman gastrointestinal tract of a single host,[18][19] from about 2–4 weeks[20] or about 4–8 weeks.[21]E. vermicularis molts four times; the first two within the egg before hatching and two before becoming an adult worm.[22]
Although infection often occurs viaingestion of embryonated eggs by inadequate hand washing or nail biting, inhalation followed by swallowing of airborne eggs may occur rarely.[19][21] The eggs hatch in theduodenum (i.e., first part of thesmall intestine).[23] The emerging pinwormlarvae grow rapidly to a size of 140 to 150 μm,[20] and migrate through the small intestine towards thecolon.[19] During this migration, theymoult twice and become adults.[19][21] Females survive for 5 to 13 weeks, and males about 7 weeks.[19] The male and female pinworms mate in theileum (i.e., last part of the small intestine),[19] whereafter the male pinworms usually die,[23] and are passed out with stool.[24] The gravid female pinworms settle in theileum,caecum (i.e., beginning of thelarge intestine),appendix andascending colon,[19] where they attach themselves to themucosa[21] and ingest colonic contents.[25]
Almost the entire body of agravid female becomes filled with eggs.[23] The estimations of the number of eggs in a gravid female pinworm range from about 11,000[19] to 16,000.[21] The egg-laying process begins about five weeks after initial ingestion of pinworm eggs by the human host.[19] The gravid female pinworms migrate through the colon towards therectum at a rate of 12 to 14 cm per hour.[19] They emerge from theanus, and while moving on the skin near the anus, the female pinworms deposit eggs either through (1) contracting and expelling the eggs, (2) dying and then disintegrating, or (3) bodily rupture due to the host scratching the worm.[23] After depositing the eggs, the female becomesopaque and dies.[24] The female emerges from the anus to obtain the oxygen necessary for the maturation of the eggs.[24]
E. vermicularis causes the medical conditionpinworm infection also known asenterobiasis, whose primary symptom isitching in the anal area.[26] Extraintestinal disease is rare and most commonly involves the female reproductive tract,[27] but spleen abscess has also been reported.[28] Enterobius vermicularis infections are found to be correlated with stunting and lower meanI.Q. among prepubescent children.[29][30]
The pinworm has a worldwide distribution,[25] and is the cause of the most commonhelminthiasis (parasitic worm infection) in the United States, western Europe, and Oceania.[21] In the United States, a study by theCenter of Disease Control reported an overallincidence rate of 11.4% among children.[21] Pinworms are particularly common in children, withprevalence rates in this age group having been reported as high as 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, and 29% in Denmark.[21]Finger sucking has been shown to increase both incidence and relapse rates,[21] andnail biting has been similarly associated.[31] Because it spreads from host to host throughcontamination, pinworms are common among people living in close contact, and tends to occur in all people within a household.[25] The prevalence of pinworms is not associated with gender,[25] nor with any particular social class,race, or culture.[21] Pinworms are an exception to the tenet that intestinal parasites are uncommon in affluent communities.[21]
A fossilized nematode egg was detected in 240 million-year-old fossil dung,[32] showing that parasitic pinworms already infested pre-mammaliancynodonts. The earliest known instance of the pinworms associated with humans is evidenced by pinworm eggs found in humancoprolitescarbon dated to 7837 BC found in westernUtah.[19]
^Foitová, Ivona; Civáňová, Kristína; Baruš, Vlastimil; Nurcahyo, Wisnu (1 July 2014). "Phylogenetic relationships between pinworms (Nematoda: Enterobiinae) parasitising the critically endangered orang-utan, according to the characterisation of molecular genomic and mitochondrial markers".Parasitology Research.113 (7):2455–2466.doi:10.1007/s00436-014-3892-y.ISSN1432-1955.PMID24880237.S2CID15076891.
Hasegawa H, Ikeda Y, Fujisaki A, et al. (December 2005). "Morphology of chimpanzee pinworms, Enterobius (Enterobius) anthropopitheci (Gedoelst, 1916) (Nematoda: Oxyuridae), collected from chimpanzees, Pan troglodytes, on Rubondo Island, Tanzania".The Journal of Parasitology.91 (6):1314–7.doi:10.1645/GE-569R.1.PMID16539010.S2CID32110983.
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Nakano T, Okamoto M, Ikeda Y, Hasegawa H (December 2006). "Mitochondrial cytochrome c oxidase subunit 1 gene and nuclear rDNA regions of Enterobius vermicularis parasitic in captive chimpanzees with special reference to its relationship with pinworms in humans".Parasitology Research.100 (1):51–7.doi:10.1007/s00436-006-0238-4.PMID16788831.S2CID32762371.
Hasegawa H, Takao Y, Nakao M, Fukuma T, Tsuruta O, Ide K (February 1998). "Is Enterobius gregorii Hugot, 1983 (Nematoda: Oxyuridae) a distinct species?".The Journal of Parasitology.84 (1):131–4.doi:10.2307/3284542.JSTOR3284542.PMID9488350.
"B80: Enterobiasis".International Statistical Classification of Diseases and Related Health Problems (ICD) 10th Revision. World Health Organization. 2007. Retrieved5 December 2009.
Burkhart CN, Burkhart CG (October 2005). "Assessment of frequency, transmission, and genitourinary complications of enterobiasis (pinworms)".International Journal of Dermatology.44 (10):837–40.doi:10.1111/j.1365-4632.2004.02332.x.PMID16207185.S2CID3193432.
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